Re: why is a magnetic compass of little value inside a submarine?

In the past, the submarines were constructed with magnetic material (iron, 
steel, e.g.), what caused the compass to be of little value inside it, as 
it caused a strong interference in the measurements.

Nowadays, the submarines are made of non-magnetic materials, exactly to 
difficult its detection by magnetic measurements, and the compass could be 
used in some cases. But the navigation systems are so powerful and precise 
that a compass can not help in a significant way.

By the way, the magnetometers were developed in the II World War to be a 
powerful engine to detect submarines! With the end of the War, the 
geophysicists took the equipment to investigate the Earth.

Best regards, and sorry for the delay in answering your question.

Eder C. Molina
Geophysicist
Dept. of Geophysics
Institute of Astronomy, Geophysics and Atmospheric Sciences
Universidade de Sao Paulo
BRASIL